The penetration of toxic antigenic or enzymatic irritants from the subgingival plaque into the tissues of the gingival sulcus represents one of the most fundamental events in the initiation of inflammatory periodontal disease. Thus, the ability of the epithelium which lines the gingival sulcus to act as an effective barrier is an important mechanism of host defense. The purpose of this investigation is to evaluate mechanisms by which to improve the barrier function of sulcular epithelium. Current studies focus on the relationship between dynamic measurements of sulcular permeability in various states of gingival inflammation and the ultrastructural correlates of barrier function. A reproducable microperfusion system has been developed for the quantitative assessment of sulcular barrier function. This technique will be utilized in the systematic study of the effects of barrier active agents on gingival permeability.